1. Field of the Invention
The present invention relates to a 3-grid neutral beam source used for etching semiconductor device, and more particularly to a 3-grid neutral beam source used for etching a semiconductor device and capable of obtaining a great amount of ion flux at low energy by improving a grid structure of a conventional neutral beam source converting ion beams into neutral beams.
2. Description of the Prior Art
As generally known in the art, an ion beam source is technically used in a field requiring a uniform beam distribution over a large area. Particularly, such an ion beam source has been widely used in a semiconductor field, so as to implant impurities into a semiconductor substrate, deposit a predetermined material layer on the semiconductor, or etch a material layer formed on the semiconductor. Herein, the ion beam source ionizes gas so as to supply ion gas into a require place.
However, in a conventional etching device using the ion beam source, a great amount of ions may exist in a conventional etching device for performing an etching process and such ions may collide with a semiconductor substrate or material layers formed on the semiconductor substrate with hundreds of eV energies, thereby causing electrical damage or physical damage to the semiconductor substrate or material layers formed on the semiconductor substrate.
To solve the above problem, applicant of the present invention has filed a Patent application with Korean intellectual property office entitled “Ion beam source capable of improving ion flux”, which is now pending with Korean laid-open publication No. 2002-92482.
In the accompanying drawings, FIG. 1 schematically shows an inductively coupled RF (radio frequency) ion source 10′ having an RF coil.
Referring to FIG. 1, the inductively coupled RF ion source 10′ includes a plasma generating chamber 11′ made of quartz. In addition, a gas feeding port 19′ is formed at a top of the plasma generating chamber 11′ in order to feed reaction gas into the plasma generating chamber 11′. An inductive coil 14′ is wound around the plasma generating chamber 11′. The inductive coil 14′ is connected to an RF matchbox 12′, which is connected to an RF power supply 13′ for supplying RF power.
In addition, a dual grid assembly 15′ having a plurality of ion beam paths 150′ is provided at a bottom of the inductively coupled RF ion source 10′ in order to control an extraction of ions from the plasma generating chamber 11′.
As mentioned above, in an etching device using the ion beam source, a great amount of ions may exist in the etching device for performing an etching process and such ions may collide with a semiconductor substrate or material layers formed on the semiconductor substrate with hundreds of eV energy, thereby causing electrical damage or physical damage to the semiconductor substrate or the material layers formed on the semiconductor substrate.
To solve the above problem, applicant of the present invention has filed a Patent application with Korean intellectual property office entitled “Neutral beam etching device”, which is now allowed to applicant of the present invention with Korean Patent No. 10-412953.
The etching device disclosed in the above patent includes an ion source having a plasma generating chamber for extracting ion beams, a dual grid assembly positioned at a bottom of the ion source, and a reflective member positioned at a lower end of the dual grid assembly.
FIGS. 2A and 2B are photographic views showing variation of ion density when voltage is applied to a dual grid assembly in a neutral beam etching device disclosed in the above patent. See Appendix A for a color version of these drawings;
Referring to FIG. 2A, voltage applied to a first grid 15a′ does not sufficiently exert an influence to the plasma generating chamber, so ion density in the plasma generating chamber becomes high and an acceleration degree and a flow rate of ions passing through the ion beam paths 150′ become low.
Referring to FIG. 3B, voltage applied to the first grid 15a′ is significantly lowered at a second grid 15′, and at the same time, an amount of ion flux becomes reduced.
Accordingly, a conventional neutral beam etching device utilizing a dual grid must increase voltage applied to the grids in order to increase an amount of ions, that is, in order to increase an acceleration degree and a flow rate of ions passing through the grid assembly. Therefore, ion energy is also increased. However, if the ion energy is increased, kinetic energy of ions is also increased, so a semiconductor substrate may be damaged due to the ions making contact with the semiconductor substrate while an etching process is being carried out.